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Lily Pad Pool Warmers 

Make] Projects 

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build, hack, tweak, share, discover,- 

Lily Pad Pool Warmers 

Written By: Edward Hujsak 



Box cutter (1) 

or utility knife with sharp blades 

Clamp (1) 

to secure the 2x4 handle to the tabletop 

Drill (1) 

Scissors (1) 

Soldering iron (1) 

Spring clamps (1) 

Polyethylene film (1) 

commonly used by landscapers and 


Hula hoops (50 or more) 
You need enough to cover at least half 
your pool's surface. These can be 
purchased from school sports suppliers 
all over the web for about $2.50 per 
hoop: in my experience, the shipping 
usually costs more than the hoops. 

Metal bard) 

for the spot-welding guide. This should 

be V/2" longer than your soldering iron's 


Hose clamp (2) 

Medium-density fiberboard (MDF) (1) 
Or plywood, or particleboard for the 
assembly jig turntable. You need a disc 
the same diameter as your hula hoops, 
usually 30". 

Fir lumber (1) 

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Lily Pad Pool Warmers 

Fir lumber (2) 

Brads (8-9) 

for the assembly jig 

Carriage bolt (1) 

Metal bard) 

(optional) to cool the spot welds. 
Aluminum or steel is OK. Instead you 
could use the back of the small bar, your 
spot- welding guide, but you'll have to 
cool it in water frequently. 


Here's an easy way to warm your pool that's efficient, low-cost, safe, and actually enhances 
the beauty of the pool. The Lily Pad pool warmer doesn't need to be removed to swim, 
sweep, or vacuum, and it meets new requirements in water conservation areas to keep at 
least half of a pool's surface covered. 

Best of all, the Lily Pad pool warmer can be made by anyone who's just a bit handy with 
tools. It's made of hula hoops, with black polyethylene film stretched over them to actually 
warm the water they come in contact with. 

The Attractive Solution 

The Lily Pad pool warmer uses black (low albedo) polyethylene film stretched over hula 
hoops. The film is in contact with the water, so it captures and transmits most of the sun's 
incoming radiation directly into the pool, warming the surface of the water. Calorimetric tests 
have shown that at high noon, a single Lily Pad will transmit more than 500 BTU per hour. 

As a bonus, this solution is highly attractive. Since it doesn't need to cover the entire pool, it 
gives the appearance of a dynamic sculpture as the pads nudge each other and form 
constantly varying patterns across the surface. 

To swim, it's not necessary to remove the pads. Half the pool area is open, and the bow 
wave ahead of a swimmer causes the pads to float aside. If you want to open the entire area 
for swimming, the pads can be removed in less than 5 minutes. And they can be seasonally 

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Lily Pad Pool Warmers 

stored in the boxes in which the hula hoops are shipped. My experience has shown that it's 
also not necessary to remove the pads for sweeping or vacuuming the pool. 

Step 1 — Mod the soldering iron. 

• Polyethylene film can be easily spot-welded to hula hoops made of the same material, by 
using a slightly modified soldering iron. 

• Add a simple guide to your iron so that it self-guides along a spot-welding path that's 
uniform around the entire hoop. To do this, just add a bar that extends 1 V2" past the tip of 
the soldering iron. Clamp the small metal bar onto the barrel of the soldering iron, using a 
scrap of metal as a spacer between, so that the guide stands 2" away from the iron's tip 
(half the width of a hula hoop). Use small hose clamps to secure the guide. 

• After you've made the guide, grind the tip of the soldering iron to a flat surface of about 1" 

Step 2 — Build a jig for assembly. 

• Since an average pool may require 50 or more Lily Pads, it's handy to build a simple jig for 
quicker assembly. Made of common materials, the jig is just a long handle and a rotating 
circular platform that holds the hula hoop securely while you spot-weld the polyethylene 
film to it. 

• Cut a disc of plywood or other flat, sturdy material that's 30" in diameter (or the diameter 
of your hoops). This is your turntable. Drill a V2" hole in the center. 

• Center a hula hoop on top of the disc, and mark a circle on the disc along the inner edge of 
the hoop (about %" in from the edge). 

• Hammer in brads along the inner circle you drew, spacing them evenly about 10" apart. 

• Lay the three 2x4s flat. Drill a V2" hole in the center of each 8" length, and a V2" hole 
centered 4" from the end of the 6' length. 

• Take the 6-footer, stack the two 8-inchers on top, and lay the turntable on top of that, 
aligning all the holes. Attach them all with the carriage bolt. 

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Lily Pad Pool Warmers 

Step 3 — Prepare the black plastic and the hoops. 

• The polyethylene film circles should be cut about 1" bigger than the hula hoops all around, 
31" for a 30" hoop. Using a hoop for a template, cut out the circles with a sharp box knife 
or scissors. If needed, use a piece of cardboard under the film as a safe cutting surface. 
Cut all the film circles you need before moving on to the spot-welding. 

• I discovered the hard way that hula hoops are not watertight. Seal the joint by wrapping a 
few turns of electrician's tape around the joint and over the adjacent staples. Don't worry 
about spot-welding in this area. 

• Now we have watertight hoops and circles of black plastic ready to be united. Here's how I 
did it. 

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Lily Pad Pool Warmers 

Step 4 — Make your Lily Pads. 

• Lay the hula hoop on the rotating assembly jig. Stretch the polyethylene film over it, and 
hold the film in place using the 6 clamps, evenly spaced around the circumference. I 
marked the turntable every 60° to make spacing easier. 

• Make 2 spot welds on either side of each clamp, always holding the film taut when you're 
welding. Work from one side to the other, turning the hoop around on its rotating jig. 

• Immediately after each spot weld is made, it's necessary to flatten and cool it. This is best 
done with a 36" bar of metal laid across the diameter of the film. 

• Alternatively, you can use the back of the soldering iron guide, chilling it in water after 
every few welds. 

• Spot-weld the remainder of the film to the hoop, with spot welds about 1" apart, including 
the area under the clamps. Soon enough, the feel of the operation will become obvious. A 
little practice on a test piece is recommended. 

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Lily Pad Pool Warmers 

Step 5 

• Once the spot welding is completed, trim the overhanging film with a sharp box cutter, 
rotating the table against the knife. 

• Finally, use the tip of the soldering iron to puncture 9 small vent holes in the film, one in 
the center and the rest distributed in a circle of about 24" diameter. Without these vents, 
vapor bubbles would form under the stretched polyethylene, and lower the heat transfer. 

• You're done! Now make more. 

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Lily Pad Pool Warmers 

Step 6 — Maintenance 

• Like any pool cover, the Lily Pads 
will gather dust and dirt over time. 
The pads are easily cleaned using 
a water detergent solution, then 
rinsing. In pools where the water 
hasn't been changed for a long 
time, evaporation of water from the 
surface of a pad will leave a salt 
deposit. In this case, cleaning is 
best done with an acid solution, 
while wearing rubber gloves (1 cup 
of pool acid to 2 gallons of water, 
then rinse). Cleaning restores the 
film to a like-new condition. 
Judging from the condition of the 
Lily Pads at the end of one season, 
the useful life could be three or 
more years. 

• TIP: When using Lily Pads, 
it's best to operate the pool 
pump at night only. When the pump 
operates, the skimmer will draw 
warm water (created at the surface 
by the pads) into the filter and 
return lines, where heat is lost by 
conduction. This is true of all 
blanket pool warmers. 

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Lily Pad Pool Warmers 

Step 7 — The Pool Owner's Dilemma 

• The thermal behavior of swimming pools is complex, due to a number of factors that act to 
cool the water, while the sun and artificial means work to keep the water warm. Cooling 
forces are at work day and night, and include evaporation, conduction into surrounding 
soil, air current effects, and nighttime long wave (infrared) radiation into space. Gas-fired 
heaters are the most common pool warmers, but up-front costs for equipment and 
installation run into the thousands of dollars. And then there's the operating cost and the 
price of natural gas. 

This project first appeared in MAKE Volume 23 , page 131 . 

This document was last generated on 201 2-1 1 -03 03:1 4:36 AM. 

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